The present invention relates, in general, to apparatus for manufacturing liquid crystal displays (“LCDs”), and in particular, to an apparatus for printing bead spacers at predetermined locations on LCD substrates.
An LCD is currently one of the more widely used types of flat panel displays. An LCD includes a liquid crystal layer interposed between two transparent sheets, or substrates, having a plurality of field generating electrodes formed thereon. The LCD controls the transmission of light passing through the liquid crystal layer by rearranging the orientation of the molecules of the liquid crystal layer through the selective application of voltages to the electrodes.
Upper and lower substrates of the LCD are coupled to each other by a sealant at their periphery that seals the liquid crystal material therebetween. The upper and lower substrates are spaced apart from each other by spacers that maintain a selected “cell gap” between the substrates. The spacers can be either generally spherical “bead spacers” that are randomly scattered in an irregular pattern between the two substrates, or “columnar spacers” that are disposed in a uniform pattern therebetween.
The columnar spacers are formed by coating a photosensitive film on a color filter array panel of the display and then performing an expose-and-develop process on the film so that a desired opaque pattern is formed on the panel corresponding to, e.g., a channel unit, gate lines, storage electrode lines, and a light blocking member. Since an additional photolithography process is required during the formation of the columnar spacers, the production cost of the display unit is relatively greater than those incorporating bead spacers. Also, unlike the plastic-based bead spacers, the columnar spacers have a relatively low elasticity, and hence, can result in a relatively small LC fill margin. Accordingly, use of columnar spacers can lead to certain problems, such as LC filling failures, and “smear” failures, in which the spacers or a film on the lower surface of the upper panel is broken.
In the case of the randomly distributed bead spacers, however, the spacers can act as foreign particles that cause leakage of light from the panel and a deterioration of its contrast ratio. It is also possible for the bead spacers to move slightly and thereby cause damage to an alignment layer of the display.
To address the foregoing problems, apparatus was developed for “printing” bead spacers at predetermined locations on an LCD substrate. However, as the size of the substrate increases, the size of a spacer supply substrate and a transfer roller of the apparatus must be increased. Furthermore, when the spacer supply substrate transfers spacers to the transfer roller, spacers that are not transferred to the roller can remain in the recesses of the spacer supply substrate. Accordingly, when spacers are next transferred from the transfer roller to an LCD substrate, a manufacturing problem can arise because the spacers can be deposited in two or more layers.